1. Technical Field
The present invention relates to a cementitious matrix having high strength and containing no coarse aggregate, and a fiber reinforced cement based mixture.
2. Background Art
Conventional concrete ranges from normal concrete used for civil engineering and architectural constructions to high-fluidity concrete, high-strength concrete, mass concrete, underwater concrete, and the like according to the intended use, and is basically a material intended to be reinforced with reinforcing steel bars. Nowadays, however, there is a tendency to employ so-called fiber reinforced concrete (hereinafter, sometimes abbreviated to “FRC”) in which short fibers are incorporated into the conventional concrete for the purpose of supplementing steel bar reinforcement, preventing corner defects of members, and preventing cracking due to drying shrinkage.
The aggregates mixed in these concretes are composed of a fine aggregate and a coarse aggregate. In conventional concrete, a unit weight of aggregate contained in a unit volume of concrete is larger than a unit weight of powder (=unit weight of cement+unit weight of mineral admixture). For example, the ratio of the unit weight of aggregate to the unit weight of powder is given by 400 to 700% for the concrete that is most commonly used. It is about 250 to 300% even for the powder-type high-fluidity concrete containing a large amount of powder.
Moreover, the largest particle diameter of coarse aggregate used for conventional concrete is limited most frequently to 20 mm or 25 mm in the case of applying to general structures, and limited to 40 mm or 80 mm in the case of applying to dams and the like. Therefore, in conventional fiber reinforced concrete, the bonding mechanism between fibers and concrete does not rely on the mechanical bond through the aggregate mixed in the concrete but relies on the chemical adhesion and frictional force between concrete hydrate (cement paste) and fibers.
On the other hand, ultra-high-strength fiber reinforced concrete (hereinafter, sometimes abbreviated to “UFC”) that is obtained by mixing reinforcing fibers such as metallic fibers or organic fibers into a cementitious matrix obtained by mixing cement and pozzolanic reaction particles (pozzolanic material) into aggregate having a largest aggregate particle diameter of about 1 to 2 mm is known.
UFC has such a characteristic that it can secure a certain level of tensile strength and toughness even after development of a crack, by combining fibers having high tensile strength with a cementitious matrix being dense and having ultra-high strength. Specifically, this has been considered to be due to the exertion of a so-called bridging effect in which the fibers cover tensile force instead of the cementitious matrix when a crack is developed in the cementitious matrix as a result of the exertion of the tensile stress on the materials.
For this reason, unlike the conventional reinforced concrete, UFC does not require reinforcement with reinforcing steel bars. Moreover, concrete structures built using UFC can achieve the reduction in the thickness and the weight of the members.
On the other hand, by performing the high temperature heat curing to UFC at 80° C. to 90° C., the hydration reaction of cement, and a binder such as a pozzolanic material including silica fume, fly ash, ground blast furnace slag, and the like, which are contained in a cementitious matrix, can be completed efficiently, and in a short time, therefore, UFC is frequently subjected to heat curing.
Moreover, UFC can achieve significant improvement in the durability because denser hydrated cement particles are developed in a short time through a hydration process when the cementitious matrix is subjected to heat curing as compared with the case of the controlled normal temperature curing. Further, after the heat curing, UFC has a characteristic that drying shrinkage becomes almost zero, a creep coefficient is significantly decreased, and the like (see Patent Documents 5 to 11, and the like).
Patent Document 1 discloses that by mixing an inorganic mineral admixture composed of at least one kind of blast furnace slag, fly ash, or limestone powder into a cementitious composition of low-heat Portland cement and silica fume, a high-strength concrete excellent in the fluidity, the workability, and the strength development can be obtained at a water-cement ratio of about 12 to 30%. However, as to the inorganic mineral admixture disclosed in Examples, there are only the cases where one kind of inorganic mineral admixture is applied, and the effects of the combination of these inorganic mineral admixtures are neither described nor suggested.
On the other hand, Patent Document 2 relates to a cementitious matrix for high-fluidity spraying concrete, and discloses that one or more kinds of auxiliary powders selected from limestone powder, silica stone powder, blast furnace slag, or fly ash are added into a mixture of Portland cement and silica fume. In this document, the Examples or effects of the combination of the limestone powder with another auxiliary powder are neither described nor suggested. Further, as the effect disclosed in Patent Document 2, the reduction of a rebound ratio is only disclosed.
Each of the cementitious compositions disclosed in Patent Documents 3 and 4 has almost the same configuration as each other except for the type of cement. The difference between the two is that while the type of cement of the cementitious composition is ordinary Portland cement in Patent Document 3, the type of cement of the cementitious composition is high belite-based Portland cement in Patent Document 4. These documents disclose the effect of improving fluidity, and the reduction effect of the amount of high-range water-reducing agent that is required to obtain a certain level of fluidity of concrete, by using a cementitious composition in which each of the cement, the silica fume, and the limestone powder having a specific grading distribution is contained in an amount of specified parts by weight. Further, Patent Documents 3 and 4 disclose the effects of fluidity in the mortar and concrete in which a cementitious composition containing cement, silica fume, and limestone powder is applied, however, the Examples or effects of the combination of the cementitious composition described above with ground blast furnace slag or fly ash are neither described nor suggested. In addition, there is also no disclosure of the strength development, the shrinkage associated with cement hydration, and the effects relating to hydration heat.
Both Patent Documents 5 and 6 are the documents relating to ultra-high-strength fiber reinforced concrete. The fibers contained in a latent hydraulicity composition of Patent Document 5 are organic fibers or carbon fibers, while the fibers in Patent Document 6 are metallic fibers, and thus these Patent Documents are different in terms of fibers, but are common in the cementitious matrix. The cementitous matrices disclosed in these documents are each composed of cement, fine particles such as silica fume, and two kinds of inorganic particles A and B, in which a specific surface area and a mix proportion by weight are specified to each of the materials. Inorganic particles A and inorganic particles B are characterized in that the ranges of the specific surface area are different from each other, and examples of the material applicable to these inorganic particles A and B include slag, limestone powder, feldspars, mullites, alumina powder, quartz powder, fly ash, volcanic ash, silica sol, carbide powder, and nitride powder. Therefore, according to these documents, a mixture containing a component such as cement, silica fume, limestone powder, ground blast furnace slag, or fly ash can be acceptable. However, Patent Documents 5 and 6 focus only on the improvement of the self-compacting and mechanical characteristics (compressive strength, and flexural strength) before hardening, and in which there is neither disclosure nor suggestion focusing on, for example, the development of early strength, or the reduction of amount of autogenous shrinkage, the reduction of hydration heat, and the like in the curing stage. Moreover, Patent Documents 5 and 6 neither describe nor suggest the chemical effects obtained by the specification of the content of the limestone powder that is an inorganic powder, and the effects obtained by the combination of limestone powder with ground blast furnace slag or fly ash.
Herein, as the document disclosing the point that the ratio of flexural strength/compressive strength of an ultra-high-strength cementitious matrix is improved, there are Patent Documents, 7, 8, and 11. Patent Document 7 is characterized in that a setting retarding agent is contained to a component such as cement, pozzolan-like fine powder, and fine aggregate, and describes that the ratio of flexural strength/compressive strength is improved due to the shrinkage reduction effect of a setting retarding agent. Further, Patent Document 8 describes that the ratio of flexural strength/compressive strength is improved by containing an expansive admixture in addition to a setting retarding agent.
On the other hand, Patent Document 11 discloses that the ratio of flexural strength/compressive strength is improved by a cementitious composition in which cement is combined with silica fume, coal gasification fly ash, and plaster in an amount in the specific range, without containing a setting retarding agent and an expansive admixture. Herein, the components common to Patent Documents 8 and 11 are coal gasification fly ash and plaster. There is a description that plaster forms ettringite in needle crystals by a hydration reaction, and the ettringite fills the pores in the cement hardened body to promote the densification, and achieves the high strength. Further, there is a disclosure that the flexural strength in a cement hardened body can be improved by mixing silica fume, and coal gasification fly ash in a specific ratio.
Moreover, Patent Documents 9 and 10 each disclose a composition of a cementitious matrix composed of cement, pozzolanic reaction particles, and sand particles. Further, metallic fibers, organic fibers, composite fibers obtained by combining organic fibers with metallic fibers, or the like are contained as fibers to reinforce the flexural strength in these cementitious matrices. In addition, examples of the pozzolanic reaction particles include silica fume, fly ash, and blast furnace slag, and there is a disclosure that the pozzolanic reaction particles contribute to a long-term improvement in the mechanical properties by heat curing.
Further, Patent Document 12 discloses a high toughness and high strength mortar composition in which the high toughness, the high compressive strength, and the high tensile strength can be developed at an early stage only by controlled normal temperature curing. The UFC disclosed in Patent Document 12 is characterized by being combined with the special cement that contains C3S and C3A at a specific ratio, silica fume, and fine aggregate having a specific grading distribution. In addition, as the pozzolanic reaction particles, silica fume is only the applicable material.